1. Field of the Invention
The present invention relates to an image forming apparatus that applies a lubricant onto the surface of an image carrier to form a lubricant thin film.
2. Description of the Related Art
According to an image forming process in an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photosensitive element, which is an image carrier, using a photoconductive phenomenon and colored toner fine particles are attached to the electrostatic latent image using electrostatic force to visualize the electrostatic latent image. In general, the electrophotographic image forming apparatus includes a lubricant applying device that applies a lubricant onto the surface of the photosensitive element, which is a main member.
In recent years, the processing speed and image quality of color copiers and printers have been improved and a four-drum tandem image forming apparatus has been generally used as the electrophotographic image forming apparatus. In addition, with the rise of environmental consciousness, it is increasingly important to recycle materials, improve reliability, and increase a life span. In addition, the awareness of the amount of ozone generated and the amount of dust generated increases considering an office environment.
Therefore, in the image forming apparatus, in many cases, a charging roller that generates a small amount of ozone is used as a charging member. In some cases, a charging roller that faces a photosensitive element with a small gap therebetween is used in order to increase a life span. In many cases, in order to meet a demand for high-quality image, an AC voltage that enables a sufficient amount of charging current to flow to the charging roller and enables stabilizing a charging potential is applied to the charging roller. When an AC voltage is applied to the charging roller, the surface of the photosensitive element is damaged by a charging current. Therefore, in order to protect the surface of the photosensitive element, a lubricant is applied onto the photosensitive element.
When the lubricant is applied, the friction coefficient of the surface of the photosensitive element is reduced and the movement of the edge of a cleaning blade is stabilized. Therefore, it is possible to improve a cleaning performance. As a lubricant applying mechanism, in general, a rod-shaped lubricant is pressed against a brush roller by, for example, a spring, and the brush roller scrapes away the lubricant and applies the lubricant onto the surface of the photosensitive element. Then, a flexible blade is used to smooth the lubricant into a thin film. In addition, in many cases, a lubricant applying device is provided on the downstream side of a photosensitive element cleaning device in order to stabilize the application of the lubricant. The lubricant applying device provided on the downstream side of the photosensitive element cleaning device includes a flexible blade for applying a lubricant, separately from the photosensitive element cleaning device.
For example, Japanese Patent Application Laid-open No. 2009-116213 discloses a lubricant applying device including a lubricant applying member that applies a lubricant onto the surface of a photosensitive element and a lubricant smoothing blade that comes into contact with the surface of the photosensitive element in the counter direction, and presses and spreads the lubricant on the surface of the photosensitive element. In the lubricant applying device, the angle of a ridge that is between a lubricant smoothing blade lower surface, which faces the surface of the photosensitive element on the downstream side of a contact portion between the surface of the photosensitive element and the lubricant smoothing blade along a direction in which the surface of the photosensitive element is moved, and the lubricant smoothing blade leading end surface, which faces the surface of the photosensitive element on the upstream side of the contact portion is 90° or about 90°. The angle between a tangent line to the surface of the photosensitive element in the contact portion and the leading end surface is equal to or more than 85°.
Japanese Patent Application Laid-open No. 2006-251751 discloses a lubricant applying device in which a cleaning blade comes into contact with the surface of a photosensitive element in the counter direction, a lubricant smoothing blade comes into contact with the surface of the photosensitive element in the trailing direction, toner remaining on the surface of the photosensitive element is removed by the cleaning blade, a lubricant is applied onto the surface of the cleaned photosensitive element by a brush roller, and the lubricant smoothing blade smoothes the lubricant into a thin film on the downstream side.
Japanese Patent Application Laid-open No. 2007-127811 discloses an image forming apparatus that includes: a cleaning device including a cleaning blade which comes into contact with an image carrier by a counter method to remove toner remaining on the surface of an image carrier after transfer, a lubricant applying device which is provided with a lubricant applying member for applying the lubricant onto the surface of the image carrier, and a lubricant smoothing blade which comes into contact with the image carrier by a trailing method and spreads the lubricant applied onto the surface of the image carrier to form a thin layer, which are provided in this order from the upstream side of the image carrier in the rotational direction. The image forming apparatus further includes: a driving unit that rotates the image carrier in a direction opposite to the regular rotational direction after an image is formed; and a sheet-like antipollution member that comes into contact with the image carrier on the downstream side of the lubricant smoothing blade.
Japanese Patent Application Laid-open No. 2007-241114 discloses a lubricant applying device including a lubricant that is held on or in the vicinity of the surface of an image carrier for carrying an image and is applied onto the surface of the image carrier and an applying blade that applies the lubricant onto the surface of the image carrier. In the lubricant applying device, the lubricant is made of a lubricant material including fine particles with a volume average particle diameter of 0.1 μm to 10 μm, and the applying blade is supported so as to come into contact with the image carrier 1 at an angle (β) of 95° to 170° in the trailing direction with respect to the rotational direction of the image carrier 1.
In the lubricant applying device and the image forming apparatus, however, the lubricant smoothing blade slides on the photosensitive element while the edge of the lubricant smoothing blade is in contact with the photosensitive element. Therefore, the edge of the lubricant smoothing blade contacting the photosensitive element is worn out over time, and a performance for applying the lubricant onto the photosensitive element deteriorates. Then, the lubricant leaks out and the surface of the charging roller is contaminated by the lubricant. As a result, the electric resistance of the surface of the charging roller increases and a color streak image is formed.
In addition, the amount of lubricant applied onto the photosensitive element is insufficient and the protection of the photosensitive element is insufficient. The surface of the photosensitive element is filmed with toner and an image with uneven density is formed.
In the above-mentioned structure in which the lubricant smoothing blade comes into belly contact with the photosensitive element by the trailing method, it is possible to reduce the abrasion of the lubricant smoothing blade and improve the durability of the cleaning unit, as compared to a general edge contact structure. However, the above-mentioned structure has the following problems: a foreign material is likely to be caught in the lubricant smoothing blade, which causes the damage of the image carrier, the partial leakage of the toner and lubricant, the contamination of other process components, such as the partial contamination of the charging roller, and the formation of abnormal image due to the partial leakage of toner and lubricant.